The effect of timing of teriparatide treatment on the circadian rhythm of bone turnover in postmenopausal osteoporosis

Background: We hypothesized that with the administration of teriparatide (TPTD) treatment at different times, we would be able to modify the physiological circadian rhythm of bone turnover. Methods: The concentration of serum C-terminal telopeptide of collagen type I (beta CTX), serum N-terminal propeptide of procollagen type I (P1NP), serum ionized calcium (iCa), and plasma PTH were measured every 3 h over a 24 h period in 14 postmenopausal osteoporotic women (aged 72.4 +/- 9.3 years) treated with 20 mu g TPTD for long term, given at different times of the day. General linear model-repeated measurements (GLM RM) were performed to analyze the circadian rhythms as well as intergroup comparisons. Results: GLM-RM for both related groups showed a significant influence of time of day on all measured variables except P1NP. The analysis for each group separately provided a powerful model for beta CTX (P < 0.001, eta(2) = 0.496), serum iCa (P < 0.001, eta(2) = 0.423), plasma PTH (P < 0.001, eta(2) = 0.283), and serum PINP (P < 0.001, eta(2) = 0.248). While the evening TPTD treatment showed a marked circadian rhythm for serum beta CTX, the morning TPTD treatment rather suggested circasemidian rhythm. The P1NP rhythm followed a much smaller amplitude of the rhythm than beta CTX. Changes in serum iCa were positively related to changes in serum beta CTX (P < 0.001) and negatively related to changes in PTH (P < 0.001). Conclusion: Timing of TPTD administration may significantly change the 24 h variation in bone turnover markers as well as calcium-parathyroid axis in postmenopausal osteoporotic women.